Method of cleaning a catalytic converter

ABSTRACT

A method of cleaning an automobile catalytic converter for an automobile engine including introducing a cleaning solution containing sodium hydroxide upstream from the catalytic converter while the automobile engine is running.

FIELD OF THE INVENTION

This invention relates to the art of automotive repair, and particularly to a method of cleaning and/or refurbishing an automobile catalytic converter.

BACKGROUND OF THE INVENTION

A catalytic converter is a device used to reduce the toxicity of emissions from an internal combustion engine. Catalytic converters were first widely introduced on U.S. production automobiles for the 1975 model year to comply with tightening EPA regulations on auto exhaust. Catalytic converters are still in wide use today in motor vehicle exhaust systems and are also commonly used on other machines implementing internal combustion gasoline engines including generators, forklifts, mining equipment, trucks, buses, and trains, although catalytic converters can also be implemented with diesel engines. A catalytic converter provides an environment for a chemical reaction wherein toxic combustion by-products are converted to less toxic substances.

The first catalytic converter was invented by Eugene Houdry and is disclosed in U.S. Pat. No. 2,742,437. However, until lead was removed from gasoline, the catalytic converter was not an effective device because lead effectively poisons the catalytic converter's catalyst. Lead was previously used in gasoline to raise octane levels, but was phased out in the 1970s and 1980s due the harmful aspects of lead to people and the environment.

The catalytic converter consists of several components, the first of which is the core or substrate. The core is often a ceramic honeycomb, but stainless steel foil honeycombs are also used. The honeycomb surface increases the amount of surface area available to support the catalyst.

The second major component is the washcoat. The washcoat is a mixture of silica and alumina. The washcoat, when added to the core, forms a rough, irregular surface, which has a far greater surface area than the flat core surfaces do. The catalyst is added to the washcoat (in suspension) before application to the core.

The catalyst itself is most often a precious metal. Platinum is the most active catalyst and is widely used. It is not suitable for all applications, however, because of unwanted additional reactions and/or cost. Palladium and rhodium are two other precious metals used. Platinum and rhodium are used as a reduction catalyst, while platinum and palladium are used as an oxidization catalyst. Cerium, iron, manganese and nickel are also used, although each has its own limitations. Nickel is not legal for use in the European Union (due to reaction with carbon monoxide). While copper can be used, its use is illegal in North America due to the formation of dioxin.

There are two basic types of catalytic converters. The first is a two-way catalytic converter which has two simultaneous tasks:

1. Oxidation of carbon monoxide to carbon dioxide: 2CO+O2→2CO2

2. Oxidation of unburnt hydrocarbons (unburnt and partially-burnt fuel) to carbon dioxide and water: CxH2x+2+2xO2→xCO2+2xH2O (a combustion reaction)

This type of catalytic converter is widely used on diesel engines to reduce hydrocarbon and carbon monoxide emissions. They were also used on gasoline engines in the US market through 1981, when the two-way converter's inability to control nitrous oxides led to its replacement by three-way converters.

Since 1981, three-way catalytic converters have been used in vehicle emission control systems in North America and many other countries on roadgoing vehicles. A three-way catalytic converter has three simultaneous tasks:

1. Reduction of nitrogen oxides to nitrogen and oxygen: 2NOx→xO2+N2

2. Oxidation of carbon monoxide to carbon dioxide: 2CO+O2→2CO2

3. Oxidation of unburnt hydrocarbons (HC) to carbon dioxide and water: CxH2x+2+2xO2→xCO2+2×H2O

These three reactions occur most efficiently when the catalytic converter receives exhaust from an engine running slightly above the stoichiometric point. This is between 14.6 and 14.8 parts air to 1 part fuel, by weight, for gasoline. Generally, engines fitted with 3-way catalytic converters are equipped with a computerized closed-loop feedback fuel injection system employing one or more oxygen sensors. Within a narrow fuel/air ratio band surrounding stoichiometry, conversion of all three pollutants is nearly complete. However, outside of that band, conversion efficiency falls off very rapidly. When there is more oxygen than required, then the system is said to be running lean, and the system is in oxidizing condition. In that case, the converter's two oxidizing reactions (oxidation of CO and hydrocarbons) are favored, at the expense of the reducing reaction. When there is excessive fuel, then the engine is running rich. The reduction of NOx is favored, at the expense of CO and HC oxidation.

Catalytic converters on automobiles can be operationally damaged in two primary ways. First, catalyst poisoning occurs when the catalytic converter is exposed to exhaust containing substances that coat the working surfaces, encapsulating the catalyst so that it cannot contact and treat the exhaust. The most notable contaminant is lead, so vehicles equipped with catalytic converters can only be run on unleaded gasoline. Other common catalyst poisons include manganese primarily from the gasoline additive MMT, and silicon which can enter the exhaust stream if the engine has a leak allowing coolant into the combustion chamber. Phosphorus is another catalyst contaminant. Although phosphorus is no longer used in gasoline, it and zinc (another contaminant) was widely used in engine oil antiwear additives such as ZDDP. Beginning in 2006, a rapid phase-out of ZDDP in engine oils was begun.

Depending on the contaminant, catalyst poisoning can sometimes be reversed by running the engine under a very heavy load for an extended period of time. The increased exhaust temperature can sometimes liquefy or sublimate the contaminant, removing it from the catalytic surface. However, removal of lead deposits in this manner is usually not possible due to lead's high boiling point. Moreover, this method is inefficient, unreliable and can lead to vehicle engine damage.

The second type of catalytic converter damage is meltdown. Any condition that causes abnormally high levels of unburned hydrocarbons—raw or partially-burnt fuel—to reach the converter will tend to significantly elevate its temperature, bringing the risk of a meltdown of the substrate and resultant catalytic deactivation and severe exhaust restriction. This type of failure is generally not repairable.

Catalytic converters, due to their incorporation of precious metals, are expensive, sometimes costing $1000. However, when a catalytic converter fails, there are no accepted methods of repairing or refurbishing it. While an ineffective catalytic converter will not generally affect engine performance, it will pollute the environment and cause a vehicle to fail government-mandated emission inspections. There is a need in the art for a method of cleaning or refurbishing a catalytic converter which is both reliable and cost effective.

SUMMARY OF THE INVENTION

A method of cleaning an automobile catalytic converter for an automobile engine comprising the step of introducing a cleaning solution containing sodium hydroxide upstream from the catalytic converter while the automobile engine is running.

DESCRIPTION OF THE DRAWING

FIG. 1 is a diagrammatic view of an automobile exhaust system.

DESCRIPTION OF THE PREFERRED EMBODIMENT

While this invention is susceptible of embodiment in many different forms, there is shown in the drawings and will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to the embodiments illustrated.

The present invention provides a method of cleaning a catalytic converter to restore its effectiveness to convert harmful airborne pollutants into less harmful substances. Referring to FIG. 1, an automobile exhaust system 10 typically includes a pipe 12 with a flange 14 or other means of connection of the exhaust system to an engine. Mounted to the pipe 12 and in communication with the interior of the pipe 12 is an upstream O2 sensor 16 which senses the amount of oxygen gas within the exhaust gas after exiting the engine. Using the sensor 16 as feedback, the engine control system will adjust the air fuel ratio for the engine to generate the desired oxygen output. Attached to the pipe 14 at the opposite end from the flange is a catalytic converter 18 of the type describe above and in common use in automobiles today. The converter 18 may or may not have an air tube 20 attached thereto to provide additional oxygen for the catalytic reaction. Downstream from the catalytic converter is a second O2 sensor 22 located within a downstream exhaust pipe 24. When the O2 sensors read identical or close values, it is known that the catalytic converter is not operating properly and the engine control system will log an error. The downstream exhaust pipe 24 may optionally be attached to various mufflers 26 and resonators 28 to control the noise level of the automobile and to route exhaust to the rear of the vehicle.

In order to refurbish a system as shown in FIG. 1, the system is warmed to operating temperature (for example 200 degrees Fahrenheit) and the upstream O2 sensor 16 is removed. Second, a solution of N-Butane of from about 0-10 percent by weight and most preferably 0.1-5 percent by weight, sodium hydroxide (lye) of from about 0.1 to 10 percent by weight and most preferably 0.1-5 percent by weight, monoethanolamine of from about 0-10 percent by weight and most preferably 0.1-5 percent by weight and diethylene glycol monobutyl ether of from about 0-10 percent by weight and most preferably 0.1-5 percent by weight in a foaming liquid aerosol solution is introduced through the opening previously containing the O2 sensor 16 while the engine is running. This solution is highly basic and has a pH of about 13. Preferably, about 16 fluid ounces of solution is introduced, although more or less may be indicated based upon the condition of the catalytic converter 18. The upstream O2 sensor 16 is then replaced and error codes are removed from the engine control system. The converter is then tested by taking the automobile on a test drive.

The solution effectively removes common contaminants and allows the catalyst material to once again contact the exhaust gas to catalyze harmful compounds into less harmful compounds. As a result, the effectiveness of the catalytic converter is restored and the need to replace the converter is eliminated.

The above examples show that the invention, as defined by the claims, has far ranging application and should not be limited merely to the embodiments shown and described in detail. Instead the invention should be limited only to the explicit words of the claims, and the claims should not be arbitrarily limited to embodiments shown in the specification. The scope of protection is only limited by the scope of the accompanying claims, and the Examiner should examine the claims on that basis. 

1. A method of cleaning an automobile catalytic converter for an automobile engine comprising introducing a cleaning solution containing sodium hydroxide upstream from the catalytic converter while the automobile engine is running.
 2. The method of claim 1 further comprising the step of preheating the catalytic converter to at least 200 degrees Fahrenheit.
 3. The method of claim 1 further comprising the step of removing an O2 sensor upstream from the catalytic converter to provide an access opening to introduce the cleaning solution.
 4. The method of claim 1 wherein the cleaning solution comprises sodium hydroxide in a concentration of from about 0.1-10 percent by weight.
 5. The method of claim 1 wherein the cleaning solution comprises sodium hydroxide in a concentration of from about 0.1-5 percent by weight.
 6. The method of claim 4 wherein the cleaning solution further comprises sodium hydroxide in a concentration of from about 0-10 percent by weight.
 7. The method of claim 4 wherein the cleaning solution comprises N-Butane in a concentration of from about 1-10 percent by weight.
 8. The method of claim 4 wherein the cleaning solution comprises N-Butane in a concentration of from about 1-5 percent by weight.
 9. The method of claim 4 wherein the cleaning solution comprises monoethanolamine in a concentration of from about 0.1-10 percent by weight.
 10. The method of claim 4 wherein the cleaning solution comprises monoethanolamine in a concentration of from about 0.1-5 percent by weight.
 11. The method of claim 4 wherein the cleaning solution comprises diethylene glycol monobutyl ether in a concentration of from about 0.1-10 percent by weight.
 12. The method of claim 4 wherein the cleaning solution comprises diethylene glycol monobutyl ether in a concentration of from about 0.1-5 percent by weight. 